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Best way of "hogging out" a metal slot?

Okay, I’m tearing down the engine in my truck after running it out of oil, as I mentioned here a few days ago.

Basically, it’s been Murphy’s Law from the outset: “Whatever CAN go wrong, will.” The crisis du jour is that I need to pull the harmonic balancer. The three threaded bolt holes, however, have been exposed to the elements for so long, that the threads have rusted such that they cannot hold a bolt under the forces necessary to remove the crank pulley.

So, I felt that the best option was to drill them oversized (to 1/2") and tap a thread. Which I did, successfully, despite the tap snapping off in the last one! (Patience, plus a hammer and flathead screwdriver saved the day.) Of course, Murphy assured me that the puller has slots too narrow for a 1/2" bolt. And I can’t drill it out, with a “standard” drill, because the drill head has a narrow “sweep” and will “fall in sideways,” then torque the hell out of the whole assembly!

Left to a file, I’ve almost hogged out ONE slot, after a hour. Please tell me there’s a better way! I think I need a drill that is almost a complete “cone,” with only a bit of material cut out to dump detritus. But I don’t know if such a thing exists!

You want a conical drill bit.


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Do you have a Dremel?:

Do you have an automotive machine shop near you? I would think they could make short work of that on the cheap by using an end mill.

Know anyone with an angle grinder, a 4" or 4.5" should make short work of the slot. Much faster than a drill or dremel.

I have one of those. I have fortunately not have to use it.

Tear down in vehicle? How are u going to replace crank bearings in vehicle? How thorough is this rebuild? U have an engine puller? For ur good used motor?


What I wound up doing: instead of hogging out the puller, I took my bench grinder and put two “flat spots” on each bolt, so you can slide them on…then, by the bolt head, I spun it such that I “necked down” the diameter to 7/16 or so. That way, it would spin freely as I tightened it, and there were still 300 degrees or so of thread to hold on to, which turned out to be enough.

@Cavell, I needed to pull the crank pulley to examine and repair (if necessary) the timing gears. Also, a angle grinder wouldn’t work, because the radius was too big to fit into the slot.

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